Amputation is a painful procedure, so aggressive, multimodal analgesia is necessary. The patient should receive a premedication
that includes a pure mu agonist opioid such as morphine, fentanyl, oxymorphone or hydromorphone.
Photo 1: During a forelimb amputation, the surgeon retracts the scapula and the brachial plexus is evident. The brachial
plexus nerves should be blocked prior to cutting them.
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For hind-limb amputation, I like to use an epidural of bupivicaine and morphine. For forelimb amputations, the brachial plexus
should be blocked (Photo 1). This procedure can be performed preoperatively. However, it is frequently done intraoperatively
prior to cutting each of the large nerves. I use a mixture of lidocaine and bupivicaine. This combines the advantage of a
fast-acting block of lidocaine, so that you do not need to wait as long before cutting the nerves, with the long action of
bupivicaine.
The epineurium of each nerve is injected, using a 25-22G needle. The nerve will swell characteristically when the injection
is administered correctly and balloons out. The nerves are injected first and then the brachial artery and vein are ligated.
After ligation, the block has taken effect and you can return to cutting the nerves. If they are blocked, the muscles should
not twitch when the nerve is cut.
Post-operative pain control and post-operative support are essential. If there are no contraindications, a COX-1 sparing NSAID should be administered post-operatively. The patient also should
be maintained on an opioid or intermittent doses of oxymorphone or hydromorphone every five to six hours.
Photo 2: Post-operative photograph of a dog after a forequarter amputation. This patient has a pain-diffusion catheter in
place to provide local analgesia to the surgical site.
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Another effective method of analgesia is use of a pain-diffusion catheter. It is closed off at the end, but has multiple small
holes along the portion placed in the wound bed. Bupivicaine can be administered via the catheter every six to eight hours
to block the surgical site (Photo 2). This must be done in a sterile fashion; I remove the catheter after 24 hours to decrease
the risk of introducing bacteria.
Patients should be on intravenous fluids during surgery and post operatively at 1.5 times maintenance rates.
An in-dwelling urinary catheter and closed-collection system should be used for the first eight to 12 hours because these
patients usually are nonambulatory immediately post operatively, allowing quantification of urine production and hydration
status.
After the first 24 hours, patients can start on oral pain medications. A good combination is continuing the NSAID that was
administered parentally, along with an opioid. The opioid can be oral tramadol or a fentanyl patch. If a fentanyl patch is
used, it must be applied 12 to 24 hours before it is to be relied upon for analgesia.
Post-operative analgesia should be continued for five to seven days after the patient has gone home, depending on the pain
level.
Dr. Boston is a board-certified ACVS small-animal surgeon. She completed her residency training at the University of Guelph
and a post-doctoral fellowship in surgical oncology at Colorado State University. Her main area of interest is surgical oncology.
Dr. Boston is currently a professor of small-animal surgery at the Ontario Veterinary College, University of Guelph.
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